The present invention relates to a roller connector which rotatably retains a plurality of rollers in a line and which is incorporated into an endless roller-circulation path of an endless sliding type linear guide unit and also to an improvement in the linear guide unit of the above-type using such roller connector.
Conventionally, there has been known a linear guide unit in which a slider is movably held in engagement with a track rail through a line of endlessly circulating rollers. More concretely, this linear guide unit comprises a plurality of rollers, a track rail which is arranged on a stationary portion such as a bed and which is provided with roller rolling surfaces and a slider provided with load rolling surfaces on which the rollers roll with respect to the roller rolling surfaces of the track rail while bearing a load thereon and an endless roller-circulation path with the inclusion of the load rolling surfaces whereby the slider having a table or a mechanical apparatus mounted thereon can move freely on the track rail following the endless circulation of the rollers.
The above-described linear guide unit having the track rail and the slider held in engagement with the track rail through the rollers has the advantage of improving the load bearing capacity of the slider as compared to such type of linear guide unit that makes use of rollers while on the other hand, it has the problem that the so called skewing of the rollers (oscillatory rotation of each roller about its axis) tends to take place. Therefore, it has been an important theme in securing the smooth rotation of the rollers and hence the smooth movement of the slider within the endless roller-circulation path how to prevent the above-described skewing of the rollers.
Therefore, as a means for solving the above-described problems, there have already been provided a roller connector comprising a plurality of rollers connected together in a predetermined posture like a string of beads and a linear guide unit having an endless roller-circulation path of the slider into which the roller connector is incorporated (Japanese Patent Laid-Open No. 52217/1993). As shown in FIGS. 18 and 19, such roller connector comprises a plurality of rollers 100 arranged in a line with the axes of rotation thereof being held parallel to one another, a plurality of spacers 102 interposed among the rollers 100 and provided with concave seats 101 with which the rollers 100 come into sliding contact, respectively, and elongate flexible connecting portions 103 connecting the spacers 102 together and adapted to rotatably retain each of the rollers 100 by causing the spacers to sandwich the roller 100 therebetween from the front and rear sides thereof.
Accordingly, when such roller connector is incorporated into the endless roller-circulation path of the slider of the linear guide unit, each of the rollers 100 rolls within the endless roller-circulation path while it is retained in its predetermined posture by means of the spacers 102 from on both front and rear sides so that it is possible to cause the rollers 100 to smoothly circulate through the endless roller-circulation path while preventing the skewing of the rollers 100 and hence it is possible to make smooth the movement of the sliders with respect to the track rail.
However, in the case of the conventional roller connector of the above-described structure, there has hitherto been the possibility that the connecting portions become fatigued at an early stage of operation since the connecting portions are formed along both axial end surfaces of each of the rollers as shown in FIGS. 18 and 19, and therefore, when a force urging each of the rollers rolling through the endless roller-circulation path to skew, that is, a force oscillating the axis of rotation of each of the rollers acts on the roller, the connecting portions expand and contract in a repetitive fashion by such force.
Further, where the above-described roller connector is incorporated into the endless roller-circulation path of the slider, the sectional area of the endless roller-circulation path must be enlarged by a width corresponding to each of the connecting portions connecting the spacers together. Accordingly, if the connecting portions are present on both axial ends of each of the rollers as described above, where, for example, an endless roller-circulation path is formed by opening a roller return path in a slider, the diameter of the roller return path has to be made large so that the rigidity of the slider lowers to that degree which results in hindering the miniaturization of the slider.
The present invention has been made in view of the above-described problems.
Accordingly, an object of the invention is to provide a roller connector which can rotatably and stably retain a plurality of rollers in a predetermined posture for a prolonged period of time within an endless roller-circulation path formed in a slider of a linear guide unit.
Another object of the invention is to provide a roller connector which can improve the rigidity of the slider and contribute to the miniaturization of the slider.
A further object of the invention is to provide a linear guide unit using such roller connector.
In order to achieve the above-described objects, the roller connector of the present invention comprises a plurality of rollers arranged in a line with the axes of rotation of the rollers being held parallel to one another, a plurality of spacers interposed among the rollers and each provided with a pair of concave seats with which each of the rollers comes into sliding contact and an elongate flexible connecting portion connecting the spacers together and characterized in that the connecting portion is connected to the spacers at a position at which the connecting portion divides the outer peripheral surface of each of the rollers into two substantially equal parts in the axial direction and that the connecting portion is arranged only on one side of the line of rollers.
Further, the linear guide unit of the present invention using the above-described roller connector is required to have a structure comprising a number of rollers, a track rail having roller-rolling surfaces and a slider provided with an endless roller-circulation path having load rolling surfaces on which the rollers roll with respect to the roller-rolling surface of the track rail while bearing a load and it is characterized in that the above-described roller connector is incorporated into the endless roller-circulation path with the connecting portion of the roller connector lying inside the inner peripheral surface of the endless roller-circulation path of the slider, and that the endless roller-circulation path is provided with clearance grooves by which the connecting portion of the roller connector is received and guided.
According to such technical means, as in the case of the above-described conventional roller connector, each of the rollers is embraced in front and in rear by the adjoining spacers and rolls through the endless roller-circulation path of the slider of the linear guide unit in a state in which it is retained in a predetermined posture by the spacers. Consequently, it becomes possible to effectively prevent each of the rollers from skewing within the endless roller-circulation path.
However, in the case of the conventional roller connector, the connecting portions connecting the spacers are arranged along both end surfaces of each of the rollers in the axial direction thereof so that the connecting portions tend to become fatigued due to the application thereon of a force urging the rollers to skew during rolling while, on the contrary, the connecting portion of the roller connector according to the present invention is connected to each of the spacers at a position at which the connecting portion divides the outer peripheral surface of each of the rollers into two substantially equal parts in the axial direction so that the connecting portion does not expand and contract repeatedly due to the above kind of force thereby preventing the breakage of the connecting portion resulting from the fatigue thereof.
Further, since the connecting portion is provided only on one side of the line of rollers, where the roller connector of the present invention is incorporated into the endless roller-circulation path of the slider of the liner guide unit, the sectional area of the endless roller-circulation path can be made smaller than in the case of the conventional roller connector and also where roller return paths are formed in the slider, the lowering of the rigidity of the slider can be avoided and the miniaturization of the slider can be made with ease.
At the same time, when both axial end surfaces of each of the rollers come into contact with the inner wall of the endless roller-circulation path of the slider during the rolling operation of the roller, the posture of the roller becomes unstable due to a frictional force generating between the two so that the skewing of the roller tends to take place. Accordingly, it is preferable from the above point of view that the spacers be so provided as to prevent the movement of each of the rollers in the axial direction. For example, an annular groove may be provided in the central portion of the outer peripheral surface of each of the rollers in the axial direction so that each of the spacers fits in such annular groove so as to come into sliding contact with the roller.
With the above structure, since the axial position of each of the rollers is determined by the connecting portion of the roller connector and each of the spacers, if clearance grooves for guiding the connecting portion of the roller connector are formed in the endless roller-circulation path of the slider to be incorporated with the roller connector, it will be possible to completely prevent the displacement of each of the rollers in the axial direction during the rotation thereof and to minimize the possibility of skewing of the roller.
Further, where the roller connector circulates through the endless roller-circulation path as it expands and contracts, it is preferable to form a slit in each of the spacers from the side opposite to the connecting portion so as to separate the pair of concave seats formed on both sides thereof from the point of view of allowing each of the rollers to keep its suitable posture by the spacers. Thus, by the formation of such slit in each of the spacers, even when the roller connector bends to a great degree within the endless roller-circulation path, each of the spacers can be kept in sliding contact with the outer peripheral surface of each of the rollers by widening the slit so that the roller can always keep its suitable posture. Further, the formation of the slit has the advantage that each of the rollers can be removably mounted between the adjoining spacers with ease.